1. Field of the Invention
The present invention relates to a refrigerant compressor suitable for use with an air-conditioning system of vehicles, such as motor cars. More particularly, it relates to a refrigerant compressor internally or externally provided with means for preventing a seizure of internal mechanical moving elements of the compressor due to a lack of lubrication during an initial short period immediately after a start of the compressing operation thereof.
2. Description of the Related Art
Various types of refrigerant compressors such as a swash plate type refrigerant compressor, a variable capacity wobble plate type compressor, and a scroll type rotary compressor, have been used with vehicle air-conditioning systems. Namely, In the car air-conditioning system, the refrigerant compressor of the above-mentioned type is incorporated in a refrigerating circuit, and arranged to be driven by a car engine to thus compress a refrigerant gas to be delivered toward the circuit. The compressed refrigerant gas at a high temperature and pressure state is subsequently liquefied by a condenser, and the liquefied refrigerant is thereafter expanded by an expansion valve of the circuit to become a low temperature refrigerant mist under a low pressure. The refrigerant mist is then forwarded to an evaporator of the refrigerating circuit where at a heat exchange is carried out to cool the atmospheric air passing through the evaporator. Accordingly, the evaporated refrigerant after cooling the atmospheric air is returned to the compressor as a suction refrigerant gas, via a suction throttling valve by which the amount of the refrigerant gas to be sucked by the compressor is controlled.
The above-described refrigerant compressor is provided with various mechanical portions and elements therein which must be lubricated during the operation of the compressor. For example, various radial and thrust bearings, reciprocating pistons, cylinder bores, a rotary swash plate, shoes, an inclination changeable wobbling assembly, and so on, must be lubricated during the operation of the compressor, and therefore, a lubricating oil is usually stored in the compressor so that the lubricating oil in the state of an oil mist suspended in the refrigerant gas is supplied to the mechanical moving elements by an oil distribution mechanism provided in the compressor. Nevertheless, when the refrigerant compressor is started after a long non-operation of the car air-conditioning system, often the lubricating oil is not supplied to the mechanical moving elements, because the oil distribution mechanism does not immediately operate. Accordingly, a seizure of the mechanical moving elements often occurs in a short period immediately after the start of the operation of the compressor, which results in a failure of the operation of the compressor per se.
A further description of the prior art refrigerant compressor and car air-conditioning system will be provided below with reference to FIGS. 7 through 9.
FIG. 7 illustrates a typical variable capacity rotary swash plate type refrigerant compressor according to the prior art disclosed in Japanese Unexamined Patent publication ( Kokai ) No. 1-138382. The refrigerant compressor has an axially extended cylinder block 51 in which a plurality of axially extended cylindrical bores 52 are arranged around an axis of the cylinder block 51. In each of the cylinder bores 52 is slidably received a double headed piston 53 having a radial recess opening toward the axis. A drive shaft 54 is mounted in the cylinder block 51 so that it is extended along the above-mentioned axis of the cylinder block 51, and has a tubular slide 55 slidably fitted thereon. The slide 55 has a spherical seat 55a at an end thereof, on which a rotary swash plate 57 is movably supported via a corresponding spherically bored portion 57a. The peripheral portion of the swash plate 57 is engaged with the recesses in the plurality of double-headed pistons 53 via shoes 56 having a partial spherical surface portion, and therefore, the rotation of the swash plate 57 causes a reciprocating motion of each of the double-headed pistons 53. The rotary swash plate 57 is provided with a bifurcated connecting arm 57b extended toward a front side of the compressor and having a lateral guide pin 58 fixed thereto, to be movably engaged in an elongated guide bore 54b bored in a portion of a front part 54a of the drive shaft 54. Namely, when the slide 55 is slid on the drive shaft 54, the swash plate 57 is able to change an angle of inclination thereof with regard to a plane perpendicular to the axis of the drive shaft 54, because the guide pin 58 of the swash plate 57 is moved under the guidance of the guide bore 54b. The center about which the swash plate 57 performs the inclining motion is located so that the reciprocating motion of the double-headed pistons 53 occurs in a manner such that the top dead center of each piston 53 in the corresponding cylinder bore 52 on the rear side is always unchanged. During the reciprocating motion of the double-headed pistons 53 within the cylinder bores 52, to compress a refrigerant gas, a reacting force acts on each of the pistons 53 in response to a compression of the refrigerant gas, and this reacting force generates a moment "M" which always urges the swash plate 57 to reduce the angle of inclination thereof. As a result, a plunger 60 arranged on the rear side of the compressor is constantly axially urged toward the rear side, i.e., to the right in FIG. 7, via the slide 55.
The compressor is also provided with a front housing 50a and a rear housing 50b, each defining therein a suction chamber for receiving the refrigerant gas before compression, and a discharge chamber for receiving the refrigerant gas after compression. The rear housing 50b also defines a control chamber 59 in which the above-mentioned plunger 60 is axially movably fitted and has a circular pressure receipt surface facing the control chamber 59. The control chamber 59 is fluidly connected to a directional control valve 63 by which either a discharge pressure "Pd" from the rear discharge chamber or a suction pressure "Ps" from the front and rear suction chambers is introduced in to the control chamber 59. The discharge or suction pressure in the control chamber 59 urges the plunger 60 toward the front side, i.e., to the left in FIG. 7, and therefore, the plunger 60 has a tendency to occupy a position where at the above-mentioned axially opposite two urging forces are balanced. This position changes in response to a change in each of the two urging forces, and as a result, the angle of inclination of the swash plate 57 is set depending upon the position occupied by the plunger 60; the angle of inclination of the swash plate 57 determines the discharge capacity of the compressor.
When the above-described rotary swash plate type refrigerant compressor is used with a car air-conditioning system, the compressor is incorporated in a refrigerating circuit of the system and is driven by the car engine, when connected to the car engine via an electromagnetic clutch.
FIG. 8 illustrates an example of the car air-conditioning system according to the prior art. The air-conditioning system includes indispensable elements such as a refrigerant compressor 100, e.g., the compressor of FIG. 7, a condenser 101, an expansion valve 102, an evaporator 103, a suction throttling valve mechanism 104, and refrigerant circulating conduits interconnecting these elements. A compressed refrigerant gas at a high temperature and a high pressure is delivered from the delivery side of the compressor 100 into the refrigerating circuit and liquefied by the condenser 101, and the liquefied refrigerant is then expanded by the expansion valve 102 to become a low temperature mist under a low pressure. The refrigerant mist cools the atmospheric air when the mist is passed through the evaporator 103, and thereafter, returns to the suction side of the compressor 100 via the suction throttling valve 104, which controls the amount of the refrigerant gas to be sucked by the compressor 100. In FIG. 8, solid arrow lines indicate the stream of the refrigerant gas with respect to the compressor 100.
In the car air-conditioning system, when the compressor 100 is started after a long non-operation of the system, a seizure of the internal portions and elements of the compressor 100 to be lubricated, e.g., particularly the contacting portions between the double-headed pistons 53 and the cylinder bores 52 slid by and between the spherically bored portion 57a of the swash plate 57 and the spherical seat 55a of the slide 55, and the contacting portions between the shoes 56 and the recessed portions of the double-headed pistons 53, occurs due to a lack of lubrication. Namely, when the car air-conditioning system is not operated for a long time, the refrigerant gas in the compressor 100 is gradually liquefied under the influence of temperature differences among respective portions in the system, and accordingly, a lubricant component in the state of an oil mist suspended in the refrigerant gas is completely separated from the liquefied refrigerant. In this state, when the compressor 100 is suddenly started at a high speed, the lubricant oil in the compression chambers 64 and 65 of the cylinder bores 52 is forcibly driven out of the compressor toward the external refrigerating circuit of the air-conditioning system, and therefore, the compression chambers cannot be lubricated until the driven lubricating oil is returned to these chambers after circulating through the refrigerant circuit. Further, the lubricating oil reserved in the bottom of the compressor cannot provide the compression chambers 64 and 65 and the other internal mechanical portions of the compressor with sufficient lubrication immediately after the start of the compressor. More specifically, in the compressor 100, which uses an oil mist suspended in the refrigerant gas for lubricating the internal mechanical portions and elements thereof, the following phenomenon shown in the graph of FIG. 9 ( the abscissa indicates the time of the operation of the compressor 100, and the ordinate indicates a suction pressure of the compressor 100 ) unavoidably appears. Namely, in the graph of FIG. 9, when the compressor 100 is started at a high speed at a time T.sub.1 after a long non-operation of the compressor 100, since the refrigerant gas cannot immediately flow to the suction side of the compressor from the evaporator 103 of the refrigerating system, a suction pressure Ps of the compressor 100 shows an immediate and extreme drop for a short time .DELTA.t, and therefore, a supply of the lubricating oil to the internal mechanical portions of the compressor to be lubricated is not carried out during the time .DELTA.t. Accordingly, a seizure of the mechanical portions easily occurs during the time .DELTA.t when the compressor 100 is started after a long non-operation of the car air-conditioning system.